Polyolefin/copolyamide RF active adhesive film

ABSTRACT

Flexible, halogen-free, high frequency-sealable films fabricated from a blend of a copolyamide and a polyolefin having a carboxylic acid or carboxylic acid anhydride functionality have sufficient copolyamide to yield a DLF of at least 0.05 at a frequency of 27 megahertz and serve as effective substitutes for flexible polyvinyl chloride films. The films may be mono-layer films or multi-layer films, especially where the high frequency-sealable films serve as outer or skin layers in multi-layer films. Products made from such mono-layer and multi-layer films find utility in a number of applications, especially for medical device applications.

CROSS-REFERENCE STATEMENT

[0001] This application is a divisional of U.S. application Ser. No.09/804,114, filed Mar. 12, 2001, which claims benefit of priority fromU.S. Provisional Application No. 60/203,715, filed Mar. 12, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to radio frequency (RF) susceptible,film-forming, polymer blend compositions, especially to compositionsthat are substantially free of halogen-containing polymers such aspoly(vinyl chloride) or PVC. In other words, current analyticaltechniques do not reveal the presence of detectable quantities ofchemically combined halogen. The invention particularly relates tomono-layer films fabricated from such compositions and coextrudedmulti-layer film structures incorporating at least one layer fabricatedfrom such compositions. The invention more particularly relates to suchcompositions that comprise a copolyamide and an acid-functionalizedpolyolefin, and their use in such films and structures.

BACKGROUND OF THE INVENTION

[0003] Products manufactured from flexible PVC (f-PVC) enjoy a longhistory of use in a variety of end use applications, including thosethat rely upon its RF sealing capability, vapor or gas barriers, orflexibility. Concerns about the environmental impact of halogenatedpolymers such as f-PVC, particularly during their manufacture anddisposal, spark efforts to develop halogen-free alternatives. Phthalateplasticizer use in f-PVC, typically at levels of 10-40 percent by weight(wt %), based on composition weight, triggers debates when f-PVC findsits way into medical products, toys for children and food packaging. Thedebates center upon the tendency of plasticizers to migrate from, orleach out of, f-PVC in use or over time.

[0004] Efforts to counter the concerns tend to focus upon olefinpolymers such as polypropylene (PP), polyethylene (PE), styrenic blockcopolymers such as styrene/ethylene butene/styrene or (SEBS), andethylene copolymers such as ethylene/octene-1 or ethylene/vinyl acetate(EVA) copolymers. The olefin polymers match or approximate many physicalproperties exhibited by f-PVC and do so at a comparable cost. Filmsformed from such polymers require heat sealing as they have too low adielectric loss factor (DLF) to facilitate high frequency (HF) sealingin general or RF sealing in particular.

[0005] Literature references describe various halogen-free polymers withdielectric properties that permit HF or RF welding or sealing. Suchpolymers include, for example, thermoplastic polyurethane (TPU);polyamide (nylon) and glycol modified polyester (PETG). However, thesepolymers cost more than PVC, making direct substitution for f-PVCeconomically unattractive. In addition, some alternate RF activepolymers have a significantly higher tensile modulus or stiffness thanf-PVC, making substitution in flexible film packaging or bagapplications unfeasible.

[0006] Copolyamides, known to be RF active, suffer drawbacks in terms ofinadequate physical properties and high cost relative to f-PVC. Highnumber average molecular weight (M_(n)) polyamides, also known as nylon,generally have a high enough modulus to classify them as stiff relativeto f-PVC, and are both difficult to seal and expensive. Low M_(n)copolyamides, such as those used in the present invention, typicallyfind use in low viscosity hot melt adhesives. As such, they have lowmelt strength, low tensile strength, poor processability on conventionalextrusion equipment, adhesive type tackiness, and excessive cost.

[0007] Another effort to replace f-PVC with halogen-free polymers usescopolymers of olefins with acrylic acid esters (acrylates) or vinylesters such as vinyl acetate (VA). Copolymers with higher levels(generally greater than (>) 15 wt %, based upon copolymer weight) of VAor methyl acrylate with ethylene, provide some measure of RF activity.While such olefin copolymers exhibit tensile and modulus propertiessimilar to those of f-PVC and are of lower cost than TPU, nylon andPETG, they have a DLF significantly lower than that of f-PVC. The lowerDLF effectively requires an increase in RF generator size with aconcomitant increase in both capital expenses and power usage. Theseincreases, when coupled with longer welding times, result in a higherfinal part cost.

[0008] An effort to avoid resorting to larger RF generators involvesblending RF active inorganic or organic particulate additives, typicallyat high loading levels, into film-forming olefin polymer compositions.EP 193,902 discloses RF-sensitized compositions that include inorganicadditives such as zinc oxide, bentonite clay, and alkaline earth metalaluminosilicates at levels of 1 to 20 wt %, based on composition weight.Patent Cooperation Treaty (PCT) Application Number WO 92/09415 describesincorporating RF receptors such as phosphonate compounds, phosphatecompounds, quaternary ammonium salts, polystyrene sulfonate sodium salt,alkaline earth metal sulfate, and aluminum trihydrate into thermosetcompounds and films. U.S. Pat. No. 5,627,223 discloses adding 1 to 50 wt% of starch (to impart RF weldability) to a polyolefin blend that alsocontains a coupling agent. Such additives improve RF weldability, but doso while adversely affecting other properties such as film optics andclarity, tensile strength and toughness.

[0009] WO 95/13918 discloses multi-layer structures that include a RFsusceptible layer based on four components. The components are apropylene-based polymer, a non-propylene polyolefin, a RF-susceptiblepolymer, and a polymeric compatibilizing agent. The RF-susceptiblepolymer may be any of EVA, EMA, ethylene/vinyl alcohol (EVOH),polyamides (including nylons), PVC, vinylidene chloride polymers,vinylidene fluoride polymers, and copolymers of bisphenol A andepichlorohydrins. The compatibilizing agent is a styrene/hydrocarbonblock copolymer, preferably an SEBS block copolymer modified by a maleicanhydride (MAH), epoxy or carboxylate functionality.

[0010] WO 96/40512 discloses multi-layer structures comprising a skinlayer, a barrier layer and a RF-susceptible layer. A combination of fourpolymers yields the RF-susceptible layer. The polymers are a propylenepolymer, a non-propylene polyolefin, a RF-susceptible polymer and apolymeric compatibilizing agent. The RF-susceptible polymer may be anEVA or an EMA copolymer with a sufficient comonomer content, apolyamide, an EVOH copolymer, PVC, vinylidene chloride, a fluoride or acopolymer of bisphenol-A and epichlorohydrin. Styrene/hydrocarbon blockcopolymers, especially SEBS block copolymers modified with maleicanhydride (MAH), epoxy or carboxylate functionalities, serve as suitablecompatibilizing agents.

[0011] WO 95/14739 discloses polymeric compositions suitable for use inarticles such as medical packaging. The compositions comprise a heatresistant polymer, a RF-susceptible polymer and a compatibilizingpolymer. The RF susceptible polymer may be selected from either of twogroups of polar polymers. One group includes ethylene copolymers whereinthe comonomer is selected from acrylic acid, methacrylic acid, esterderivatives of acrylic acid or methacrylic acid with alcohols having1-10 carbon atoms (C₁₋₁₀), vinyl acetate and vinyl alcohol. The othergroup includes copolymers with segments of polyurethane, polyester,polyurea, polyimide, polysulfone or polyamide. The compatibilizer may bea styrenic block copolymer (e.g. SEBS), preferably MAH-functionalized.

[0012] European Patent Application (EP) 0 688 821 discloses a polyolefincomposition that can be formed into sheets and films sealable withRF-generated dielectric heat. The composition comprises a heterophasicolefin polymer and 3-15% of at least one polymer having a dielectricheat loss factor (DHLF or DLF) of at least (≧) 0.01. The heterophasicolefin polymer comprises a crystalline propylene homopolymer orcopolymer, an optional crystalline ethylene copolymer, and anelastomeric ethylene/propylene (EP) copolymer. The heterophasic olefinpolymer may be modified with 0.03 to 0.3% of at least one polar monomer,such as MAH. Polymers meeting the DHLF requirement include polyamides,vinyl polymers, polyesters and polyurethanes. Polyamides, especiallythose having a M_(n)≧1000, are preferred.

SUMMARY OF THE INVENTION

[0013] A first aspect of the present invention is a polymericcomposition suitable for fabrication into a RF weldable film structure,the composition consisting essentially of a blend of a copolyamide and apolyolefin that has a carboxylic acid or carboxylic acid anhydridefunctionality, the blend having a DLF of at least 0.05 at a frequency of27 megahertz (MHz) at 23° C. the copolyamide being present in an amountwithin a range of 20 to 80 percent by weight based on total blendweight.

[0014] Such polymeric compositions combine desirable characteristics ofpolyolefins (physical strength, processability and relatively low cost)with copolyamide RF activity to yield novel RF weldable film structures.The acid- or acid anhydride functionality appears to providecompatibility between two otherwise incompatible polymers, therebyleading to desirable blend homogeneity and consequent improved filmproperties relative to blends prepared from equal amounts of the samecopolyamide and a non-functionalized polyolefin (the same polyolefin butwithout an acid or acid anhydride functionality).

[0015] A second aspect of the present invention is a RF weldable filmstructure comprising at least one layer formed from the polymericcomposition of the first aspect. The film structure may be monolayer ormultilayer. Multilayer structures may include one or more layers with aDLF of less than (<) 0.05 at a frequency of 27 MHz at 23° C.

[0016] A third aspect of the present invention is an article ofmanufacture fabricated from the film structure of the second aspect, thearticle being selected from the group consisting of bags, containers,packages, automotive interior trim fabrics and parts, flotation devices,tarps and tent coverings. Other suitable applications, some of which aremore specific examples of the foregoing, include for example, medical orurological collection bags, medical ostomy bags, medical infusion orintravenous (IV) bags, inflatable devices such as air mattresses,flotation devices or toys, food packaging, retail product blisterpackaging, children's articles and toys, reinforced laminates for tentsand tarpaulins, roofing membranes and geotextiles, and stationeryapplications such as binder covers. Compositions that yield the films ofthe present invention can also be extruded into tubing with a RF activeouter layer. Such tubing can readily be used in conjunction with RFweldable films to provide a complete RF welded polyolefin film structuresuch as a medical collection bag. Skilled artisans can easily expandthis illustrative listing to include virtually any device or applicationthat requires a HF or RF sealable, flexible, mono-layer or multi-layerfilm structure. The relatively low (compared to f-PVC) cost ofpolyolefin materials used to make the films of the present invention andthe performance features of such film opens many opportunities forreplacement of flexible, plasticized, halogenated films such as f-PVC.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Unless otherwise stated, each range includes endpoints used toestablish the range.

[0018] The blend has a polyamide content sufficient to provide the blendwith a DLF ≧0.05, preferably ≧0.10 at 27 MHz when tested at 23° C. Thepolyamide content is desirably ≧20 wt %, based on blend weight,preferably ≧30 wt %. Blends having such a polyamide content lead toshort RF weld times using standard RF welding apparatus when comparedwith blends having a lower polyamide content. RF weld times may be asshort as 0.5 to 1.0 second using a 2 kilowatt (KW) RF welding apparatus(commercially available from Callanan Company) operating at a frequencyof 27.12 MHz and fitted with a brass seal bar of 0.5 inch (in) (1.3centimeter (cm)) width by 8 in (20.3 cm length) and 4 square inch (in²)((26.4 square cm (cm²)) area.

[0019] “DLF” is a calculated value determined by multiplying amaterial's dielectric constant (DC) by its dielectric dissipation factor(DDF) (or loss tangent). The DC and DDF are readily determined byinstrumented dielectric testing methods. An especially preferred testfixture utilizes a Hewlett-Packard Impedance/Material Analyzer, model4291B coupled with a Hewlett-Packard Dielectric Test Fixture, model16453A. Dielectric properties can be measured on compression moldedplaques (2.5 in (64 millimeters (mm) diameter and 0.050 in (1.3 mm)thick) formed from a material such as a polymer or a blended polymercompound.

[0020] “HF sealability” refers to bonding of a sealable polymer to aportion of itself or to another material using electromagnetic energy orwaves over a broad frequency range of 0.1-30,000 MHz. This includes RFheating and microwave (MW) heating rather than conventional heatsealing. The HF range generically covers three frequency ranges morecommonly referred to as an ultrasonic frequency range (18 kilohertz(KHz)-1000 KHz), the RF range (1 MHz-300 MHz), and the MW frequencyrange (300 MHz-10,000 MHz). The RF and MW ranges are of particularinterest. The terms “activating”, “sealing”, “bonding”, and “welding”(and variations of each word) are used interchangeably herein.

[0021] “RF active” means a material susceptible to dielectric activationvia energy in the RF range, the application of which induces rapidheating of the material. Similarly “HF active” means a materialsusceptible to dielectric activation via energy in the HF range.

[0022] In general, skilled artisans regard a material with a DLF of<0.05 as RF or HF inactive. They classify materials with a DLF of0.05-0.1 as weakly RF or HF active. They consider materials with a DLFabove (>) 0.1 to have good RF or HF activity, and materials with a DLFabove 0.2 to be very RF or HF active. While a DLF of 0.05 may producesatisfactory results, skilled artisans typically prefer a DLF >0.1, moreoften >0.2, in order to obtain sufficient sealing by application of HFwaves in general and RF waves in particular.

[0023] Dimer acid copolyamides typically result from a polymerizationreaction between a dimer fatty acid, such as azelaic acid, and at leastone alkyl or cyclic diamine, such as ethylenediamine,hexamethylenediamine, piperazine, or propylene glycol diamine. Thecopolyamide desirably has an acid value within a range of 0.5-15(milligrams (mg) of potassium hydroxide (KOH) per gram (g) of resin) andan amine value within a range of 1-50 (mg KOH/g of resin). Thecopolyamide beneficially has a ring and ball softening point (ASTM E-28)within a range of 80 to 190°0 centigrade (° C.), and more preferably 90to 150° C. Low molecular weight copolyamides additionally have a lowviscosity and an M_(n) value of from 5,000 to 15,000. Typical Brookfieldmelt viscosities of low M_(n) copolyamides range from about 900 to about13,000 centipoise (cps), when tested at 190° C. according to ASTMD-3236. Copolyamides meeting these criteria typically find use in hotmelt adhesive compositions, such as MACROMELT® (Henkel) and UNIREZ®(Union Camp). In order to be suitable for use in the present invention,the copolyamide must have a DLF ≧0.05 at 27 MHz when tested at 23° C.,preferably ≧0.1.

[0024] Additional satisfactory low M_(n) copolyamides derive fromreaction products of caprolactam or lauryllactam and water orhexamethylenediamine and adipic acid. Although similar in chemistry tohigh M_(n) polymers known as nylon 6 or nylon 12, these copolyamides areprimarily amorphous and have melting points and M_(n) valuessubstantially lower than conventional nylon resins. Desirable amorphouscopolyamides have melting points of from 90 to 140° C. and weightaverage molecular weights (M_(w)) of from 10,000 to 25,000. They aresold under the trade name GRILTEX® (EMS-American Grilon or EMS-Chemie)as hot melt adhesives.

[0025] Because of the relatively low M_(n) and low viscosity of theherein described copolyamide resins, they are difficult to process onconventional film or sheet extrusion equipment which has been designedfor high molecular weight polymers. Additionally, the resins exhibitrelatively low tensile and tear strength properties and are tacky orsticky when extruded into monolayer films. The present blendcompositions overcome the limitations inherent in the low molecularweight copolyamide resins used in this invention.

[0026] With respect to polymers, “acid functionality” refers topolymers, particularly olefin polymers, having polymerized therein anethylenically unsaturated carboxylic acid as well as polymers resultingfrom a reaction to graft such an acid onto a polymer backbone. Suitableacids include acrylic acid (AA) and methacrylic acid (MAA). Especiallypreferred acid functional olefin polymers are those produced fromethylene-based polymers and copolymers. Commercially availableethylene/acrylic acid (EAA) copolymers include PRIMACOR* resins(*trademark of The Dow Chemical Company). Commercially availableethylene/methacrylic acid (EMAA) copolymers include those commerciallyavailable from E. I. du Pont de Nemours and Company under the tradedesignation NUCREL®. Commercially available ethylene/methylacrylate/acrylic acid terpolymers (EMAAA) include those commerciallyavailable from Exxon Chemical under the trade name ESCOR® ATX resins.The acid comonomer must be present in an amount of ≧3 wt %, preferably≧6 wt %, based on polymer weight, in order to impart sufficientcompatability of the olefin with the copolyamide. Especially preferredacid copolymers have AA or MAA content of 9 to 20 wt %. Acrylic acidgrafted polyolefins include those commercially available from BPChemical under the trade designation POLYBOND®.

[0027] Similarly, “anhydride functionality” refers to polymers resultingfrom a reaction to graft an ethylenically unsaturated carboxylic acidanhydride, such as maleic anhydride (MAH) onto a polymer backbone.Polyethylene (PE), polypropylene (PP) and ethylene copolymers, such asEVA serve as suitable backbone polymers. Commercially availableMAH-grafted (MAH-g) polyolefins include BYNEL® CXA and FUSABOND® resins(E. I. du Pont de Nemours and Company), PLEXAR® (Equistar Chemicals) andLOTADER® (Elf Atochem). Typical MAH-g polymers have a MAH content offrom 0.05 to 1.5 wt %, based on total polymer weight.

[0028] Ionomers function as suitable replacements for acid- and acidanhydride-functionalized polyolefins. “Ionomers” typically refers toionomerized metal salts of carboxylic acid copolymers, such as sodium,potassium or zinc ionomers of EAA or EMAA. Commercially availableionomers include those available under the trade designation SURLYN®from E. I. du Pont de Nemours and Company.

[0029] The ionomers and the acid- or acid anhydride-functional olefinpolymers typically have a density of 0.86-0.99 grams per cubiccentimeter (g/cc), preferably 0.89 to 0.97 g/cc, and a melt index or I₂value of 0.5-300 grams per 10 minutes (g/10 min) when tested at 190° C.and 2.16 kg (ASTM D-1238), preferably 2 to 20 g/10 min.

[0030] The polymer blends desirably have a copolyamide content of ≧20 wt% and an acid or acid anhydride functionalized polymer content of nomore than (≦) 80 wt %, based on blend weight. The copolyamide contentdesirably ranges from 20 to 80 wt % with a complementary acid or acidanhydride functionalized polymer content range of 80 to 20 wt %. Morepreferably, the copolyamide content of blends is from 30 to 70 wt %,based upon blend weight. If the copolyamide is used at levels of <20 wt%, and especially at levels <10 wt %, the blend has too low a DLF topermit easy RF welding. At copolyamide levels >80 wt %, especially >90wt %, the blend processes like a low melt strength copolyamide, isdifficult to extrude on conventional extrusion equipment and exhibitspoor melt strength, high tackiness or film blocking, and generally poorphysical properties such as tensile strength, tear and impact strength.

[0031] The acid or anhydride functionalized polymer provides the blendwith increased melt viscosity during extrusion processing, increasedfilm strength and flexibility, increased adhesive peel strength and bonddurability, and improved moisture resistance, all improvements andincreases being relative to a blend lacking such a functionalizedpolyolefin. The copolyamide component provides the blend with sufficientDLF character to impart RF weldability. The copolyamide may also impartimproved oxygen and carbon dioxide barrier properties to the blend.Additionally, the softening point of most copolyamides is >100° C., withmany being >120° C., while the melting point of most acid functionalethylene polymers is slightly above or below 100° C. Thus, thecopolyamide component of the blend can improve temperature stability andbond strength at elevated temperatures (>100° C.).

[0032] The polymer blends that form films of the present invention mayalso include one or more conventional additives that impart a functionalattribute to the films, but do not significantly detract from filmsealability via exposure to HF or RF irradiation. Such additivesinclude, without limitation, antioxidant or process stabilizers,ultraviolet (UV) stabilizers, tackifiers, fire retardants, inorganicfillers, biocides, and pigments

[0033] In addition to the copolyamide and acid functional olefin polymerrequired in polymeric compositions of the present invention, amounts ofolefin polymers and copolymers can be added to achieve desired filmattributes, as long as the composition contains ≧20 wt % copolyamide.Olefin polymers suitable for purposes of the present invention includehomopolymers, such as PE or PP, and copolymers, such asethylene/butene-1 (EB), ethylene/octene-1 (EO) or ethylene/propylene(EP). Useful non-polar olefin polymers include low density polyethylene(LDPE), linear low density polyethylene (LLDPE), ultra low densitypolyethylene (ULDPE), high density polyethylene (HDPE), polyethyleneplastomer (metallocene catalyst, 0.86-0.92 grams per cubic centimeter(g/cc) density, (mPE), PP homopolymer, PP copolymer (co-PP), EVA, EMA,ethylene/n-butyl acrylate (EnBA), ethylene/ethyl acrylate (EEA), EAA,EMAA, EMAAA, ionomerized metal salts of carboxylic acid copolymers, suchas sodium, potassium or zinc ionomers of EAA or EMAA,ethylene/propylene/diene copolymer, (EPDM), ethylene/styreneinterpolymer (ESI), EVOH, polybutene (PB), polyisobutene (PIB),styrene/butadiene (SB) block copolymer, styrene/isoprene/styrene (SIS)block copolymer, styrene/ethylene-butene/styrene (SEBS) block copolymeror MAH-g olefin polymers such as MAH-g-EVA, MAH-g-PE and MAH-g-PP andMAH-g styrenic block copolymers such as SEBS-g-MAH.

[0034] The films of the present invention may be of any gauge thatserves a given need, but typically fall within a range of from 1 to 100mils (25 to 2500 micrometers (μm)), preferably 2 to 20 mils (50 to 500μm). Any conventional film forming process may be used to fabricate suchfilms. Illustrative processes include, without limitation, an annularextruded blown film process, a slot die cast extrusion film process, andextrusion coating of one or more layers upon a film or substrate. Thefilms of the present invention can be monolayer films or function as oneor more layers of a multi-layer film construction. Such multi-layerfilms preferably result from coextrusion processes as well as laminationprocesses. Additionally, HF active blend compositions of the currentinvention can be fabricated into extruded profile shapes such as tubing.For example, a RF-weldable monolayer or coextruded, multi-layer, tubularstructure may be bonded to a film or other substrate to fabricate acomposite part such as a medical collection bag. In addition, thepolymer blend compositions described herein can be dissolved in solventor dispersed as an aqueous dispersion or emulsion and coated from aliquid phase using conventional liquid coating processes.

[0035] In a preferred embodiment of the present invention, the polymericcomposition or RF active polymer blend can be coextruded, or otherwiseassembled into a multi-layer composite, with a non-RF active or weaklyRF active polymer layer. The incorporation of a RF active layer with anon-RF layer into a coextruded film structure desirably allows theentire film to be RF welded. Especially preferred film structures of thepresent invention can be denoted as “AB” or “ABA” or “BAB” wherein the“A” layer is non-RF or weakly RF active and the “B” layer is the RFactive polymer blend composition of the present invention. Additionalnon-RF or weakly RF active layers “C” can be also incorporated, such asin a “ABC” coextrusion. Skilled artisan readily understands that thesestructures merely illustrate a wide variety of foreseeable structures.

[0036] Any of the films described herein can be sealed or welded toitself or to another substrate using a conventional HF sealer, such as aRF sealer. Commercially available RF welders, such as those availablefrom Callanan Company, Weldan, Colpitt, Kiefel Technologies, Thermatron,Radyne and others, typically operate at a frequency of 27.12 MHz. Twoless frequently used radio frequencies are 13.56 MHz and 40.68 MHz.Typical MW sealing or welding apparatus function at frequencies of 2450MHz (2.45 gigahertz or GHz), 5.8 GHz and 24.12 GHz. When using RFsealers, the die or tooling can operate at ambient room temperature(nominally 23° C.) or can be preheated to temperatures such as 40° C. or60° C. Slightly elevated temperatures can improve RF activation andreduce seal time.

[0037] RF or MW activation (sealing and bonding) offers a performanceadvantage over conventional thermal or heat sealing when rapid sealingbecomes a dominant factor, such as is the case in high speedmanufacturing. HF (including RF and MW) bonding technologies allowenergy to be concentrated at the HF active layer, thus eliminating aneed to transfer heat through an entire structure. This advantagebecomes more evident with increasing film gauge, particularly forrelatively thick (gauge >5 mils or 125 μm) films where conventionalthermal sealing techniques require relatively (compared to RF sealing)long contact times to permit thermal transfer through the film to thebonding interface. For example, RF sealing can occur in as little as 0.4second whereas conventional thermal contact or impulse sealing of a filmhaving the same thickness typically requires at least several seconds toattain a comparable seal. HF bonding or sealing also has an advantageover conventional thermal sealing when a composite structure contains athermally sensitive material, such as a color sensitive dyed fabric ornonwoven material or an oriented film that can soften and undesirablyshrink upon heating. RF dies can also be fabricated in very complexshapes, a difficult task when dealing with thermal sealing equipment.

[0038] The films of the present invention facilitate fabrication of avariety of structures via HF sealing. For example, a film can be foldedover and at least partially HF sealed to itself to form a bag or apouch. Two plies of the same film readily form a like bag or pouchwithout a fold. HF sealing also promotes bonding of such a film to asubstrate such as a different film, a nonwoven fabric, an injectionmolded or extruded part, or paper. For most applications, sufficient HFsealing or bonding equates to an adhesive strength of at least 4 poundsper inch (lb/in) (0.72 Newton per millimeter (N/mm)). Medical collectionbags or drainage pouches require that an RF weld between two plies offilm have a strength that exceeds tear strength of the film itself. Inother words, an effort to peel the films apart results in tearing atleast one of the films. An RF weld or seal adhesive strength of at least4 lb/in (0.72 N/mm), as tested by the 180 degree (180°) peel test ofASTM D-903, meets this requirement. Thicker film structures, such asthose used for inflatable applications, generally require even greaterweld or bond strengths. Films similar to those of the present invention,but with a DLF <0.05, do not facilitate HF sealing and typically yieldpeelable seals that fail the above adhesive strength requirements whenexposed to the same level of HF radiation.

[0039] Notwithstanding emphasis upon HF weldability, film structures orfilms of the present composition can also be thermally laminated, sealedor welded using conventional thermal processes such as hot rolllamination, flame lamination, and heat sealing. With this capability,one can combine a thermal process with HF welding. One illustration ofsuch a combination involves a first step of thermally laminating a filmof the present invention to a substrate such as a fabric thereby forminga film/fabric composite and a second, sequential step of HF welding twocomposites together at a film/film interface, thereby providing filminterior surfaces and fabric exterior surfaces. Additional substrates ofinterest onto which films of the present invention can be laminatedinclude cellular foams, such as polyurethane or polyolefin foams, wovenor nonwoven fabrics, paper or paperboard products, thermoplastic film orsheet, wood veneer or wood products, and wood or cellulosic composites.

[0040] The following examples illustrate, but do not limit, the presentinvention. Arabic numerals or combinations of Arabic numerals andletters of the alphabet denote examples (Ex) of the present invention.Letters of the alphabet standing alone represent comparative examples(Comp Ex).

Ex 1—DLF Determination

[0041] Subject several polymer materials to DLF testing using theapparatus and procedure detailed above. The materials and theircorresponding DLF values are as follows: LDPE (LDPE 501, 0.922 g/ccdensity, melt index of 1.9 g/10 min, The Dow Chemical Company)<0.001;EAA with a 9.7 wt % acrylic acid (AA) content (EAA-1) (PRIMACOR* 1430,melt index of 5 g/10 min, The Dow Chemical Company)=0.003; EAA with a 20wt % AA content (EAA-2) (PRIMACOR* 5980, melt index of 300 g/10 min, TheDow Chemical Company)=0.007; EAA with a 9.7 wt % AA content (EAA-3)(PRIMACOR* 3460, melt index of 20 g/10 min, The Dow ChemicalCompany)=0.007; copolyamide number 1 (CPA-1) (MACROMELT® 6211,Henkel)=0.221; CPA-2 (MACROMELT® 6238, Henkel)=0.082; CPA-3 (MACROMELT®6206, Henkel)=0.057; CPA-4 (GRILTEX® 1G, EMS-Chemie)=0.11; CPA-5(GRILTEX® D1330, EMS-Chemie)=0.07; CPA-6 (GRILTEX® D1472,EMS-Chemie)=0.08; blend number 1 (B-1), a blend of 80% EAA-1 and 20%CPA-1=0.03; B-2, a blend of 60% EAA-1 and 40% CPA-1=0.06; and B-3, ablend of 40% EAA-1 and 60% CPA-1=0.083; ionomer-1 (SURLYN® 1605, E. I.du Pont de Nemours and Company)=0.008; Ionomer-2 (SURLYN® 1702, E. I. duPont de Nemours and Company)=0.003.* Means Trademark of The Dow ChemicalCompany.

Ex 2—Monolayer Film Seal Testing

[0042] Use a conventional slot die cast film line with a 2.5 in (6.4 cm)diameter, 24:1 length to diameter ratio (L/D) single screw extruderoperating at a temperature of 300° Fahrenheit (° F.) (149° C.) and a 28in (71 cm) wide slot die operating at a temperature of 300° F. (149° C.)to cast a melt-processible polymer composition onto a chilled (75° F.(25° C.)) casting roll to form a 4 mil (102 μm) monolayer film andthereafter wind the film into a roll. The melt-processible polymercompositions include 3 parts by weight (pbw) of CN-744 antiblockconcentrate (20 wt % SiO₂ in LDPE) and 2 pbw of CN-4420 slip/antiblockconcentrate (20 wt % silicon dioxide (SiO₂), 4 wt % stearamide and 4 wt% erucylamide in an EVA carrier) per 100 pbw of polymer. SouthwestPlastics supplies the latter two materials.

[0043] Dielectrically seal two plies of each film together using aCallanan 2.0 kW RF welding machine operating at 50% power setting fittedwith a non-heated 0.5 in (1.25 cm) wide by 8 in (20.3 cm) long bar sealdie and a one second seal time. Cut the film into 1 in (2.5 cm) widestrips perpendicular to the seal. Subject the strips to 180° peeltesting using an Instron tensile tester at a pull rate 12 in/min (30.5cm/min) in accordance with American Society for Testing and Materials(ASTM) test D-903.

[0044] The film compositions and corresponding seal strengths are asfollows: 100% EAA-1-no measurable seal; 80% EAA-1/20% CPA-1=4.15pounds/inch (lb/in)/0.73 Newtons/millimeter (N/mm); 60% EAA-1/40%CPA-1=4.75 lb/in (0.83 N/mm); and 40% EAA-1/60% CPA-1=>6 lb/in (1.05N/mm). CPA-1 has a ring and ball softening point of 145° C., an acidvalue of 2-10 mg KOH/g resin, an amine value <2 mg KOH/g resin, and meltviscosity of about 5,000 cps at 190° C.

[0045] The peel test data demonstrate that while a polyolefin film withno copolyamide typically cannot be RF sealed, blending as little as 20wt % of a copolyamide with a polyolefin leads to satisfactory adhesionstrength. Increasing copolyamide levels (e.g. 40 wt % and 60 wt % CPA-1)lead to stronger adhesion strength ratings.

Ex 3

[0046] Prepare a monolayer copolyamide/polyolefin blend 5.0 mil (125 μm)film on a conventional blown film line using a 1 in (2.5 cm) diameterextruder feeding into a 1 in (2.5 cm) diameter die. Ramp the extruderzone temperatures from 280° F. (138° C.) to 330° F. (165° C.) with thedie operating at 330° F. (165° C.). The film comprises 55% BYNEL CXA3101 (E. I. du Pont de Nemours and Company, acid modified EVA resin with3.5 g/10 minute melt index, 0.96 g/cc density), 30% CPA-1, 10% LDPE 501I(same as in Ex 1) and 5% CN734 antiblock concentrate (SouthwestPlastics, 15% SiO₂ in LDPE). The resulting film exhibits a machinedirection (MD) ultimate tensile strength of 1360 psi (9.4 N/mm²),ultimate elongation of 560%, 2% secant modulus of 5,020 psi (34.6N/mm²), Elmendorf tear strength 160 g/mil (6.3 grams per micrometer(g/μm) and Spencer impact strength of 270 g/mil (10.5 g/μm). The filmhas a DLF of 0.08.

[0047] Dielectrically seal two plies of the film together as in Ex 2,but with a 0.5 second low power preheat and 1.0 second RF seal timefollowed by 0.5 second dwell time (no power) and a Clayton air capacitorplate setting of 22. This yields a high strength seal (>6.0 lb/in (1.05N/mm)). The seal is strong enough to promote film breakage before seal 5failure.

Ex. 4

[0048] Replicate Ex 3, but with a blend of 40 wt % EAA-1, 40 wt % CPA-1,15 wt % of the same LDPE as in Ex 3 and 5 wt % of the same antiblockconcentrate as in Ex 3. The film has a MD ultimate tensile strength of1560 psi (10.8 N/mm²), ultimate elongation of 530%, 2% secant modulus of7,050 psi (48.6 N/mm²), Elmendorf tear strength 160 g/mil (6.2 g/μm) andSpencer impact strength of 260 g/mil (10.1 g/μm).

[0049] Dielectric sealing of two plies of the film together yields apeel strength >5.5 lb/inch (1.0 N/mm).

Ex 5

[0050] Replicate Ex 3, but with a blend of 75 wt % SURLYN® 1605 (E. I.du Pont de Nemours and Company), 20 wt % CPA-1, and 5% of the sameantiblock concentrate as in Ex 3. The film exhibits a machine direction(MD) ultimate tensile strength of 2640 psi (18.2 N/mm²) ultimateelongation of215%, 2% secant modulus of 27,300 psi (188.3 N/mm²), andSpencer impact strength of 300 g/mil (11.7 g/μm). The film has a DLF of0.06.

Ex 6

[0051] Coextrude a 3-layer 7.4 mil (188 μm) film using a conventionalupward blown film line equipped with a 5 in (12.7 cm) diameter die andthree 2.5 in (6.4 cm) extruders. The film has a symmetrical ABAstructure where the innermost and outermost layers “A” comprise 15% each(1.1 mil, 28 μm) of the overall film gauge and the core “B layercomprises 70% (5.2 mi, 131 μm) of the film thickness. The skin “A”layers comprise 95 wt % EAA-1 and 5 wt % of the same antiblockconcentrate as in Ex 3. The “B” or core layer comprises 60 wt % EAA-1and 40 wt % CPA-1. All three extruders are zone ramped from 275° F.(135° C.) to 330° F. (16620 C.) with the die zones set at 330° F. (166°0C.) This produces a 16 in (41 cm) wide lay-flat bubble. The resultingfilm has a Spencer impact Strength of 595 g/mil (23.2 g/μm), an oxygentransmission rate (O₂TR)of 375 cc-mil/100 in²-day (147 cc-mm/m²-day),and a water vapor transmission rate (WVTR) of 4.1/g-mil/100 in²-day(1.62 g-mm/m²-day). Table I below presents additional film physicalproperty data (measured in both MD and transverse direction (TD)). TABLEI MD TD Ultimate Tensile Strength 2640/18.2 2295/15.8 (psi/(N/mm²))Ultimate Elongation (%) 470 540 2% Secant Modulus 7540/52.0 7520/51.9(psi/(N/mm²)) Elmendorf Tear Strength 250/9.8  350/13.6 (g/mil/(g/μm))

[0052] Core layer “B” has a DLF of 0.06. Dielectrically seal two pliesof the film together as in Ex 3 but with a 1.5 second (sec) RF seal timeand a Clayton air capacitor plate setting of 23. The resulting seal hasa peel strength of >7.1 lb/in (1.2 N/mm), with the film breaking priorto seal failure.

Ex 7

[0053] Replicate Ex 6 to prepare a coextruded, asymmetrical (ABconfiguration) 2-layer 9.0 mil (228 μm) film but use two extrudersrather than three. Layer “A”, nominally the innermost layer, provides50% (4.5 mil, 114 μm) of the overall film gauge and has the samecomposition as Layer A of Ex 6. Layer “B”, nominally the outermostlayer, provides 50% (4.5 mil, 114 μm) of the overall film gauge andcomprises 55 wt % EAA-1, 40 wt % CPA-1 and 5 wt % of the antiblockconcentrate of Ex 3. The resulting film has a Spencer impact Strength of590 g/mil (23.0 g/μm), an O₂TR of 330 cc-mil/100 in²-day (130cc-mm/m²-day), and a WVTR of 2.4 g-mil/100 in²-day (0.95 g-mm/m²-day).Table II below presents additional film physical property data (both MDand TD). TABLE II MD TD Ultimate Tensile Strength 2930/20.2 2670/18.4(psi/(N/mm²)) Ultimate Elongation (%) 475 495 2% Secant Modulus9970/68.8 9620/66.3 (psi/(N/mm²)) Elmendorf Tear Strength  240/9.4 295/11.5 (g/mil/(g/μm))

[0054] Outer layer “B” has a DLF of 0.06. Dielectric sealing of twoplies of the film together using the same conditions as those of Ex. 6,with “B” layers adjacent to each other yields a peel strength of >5.0lb/in (0.9 N/mm).

What is claimed is:
 1. A polymeric composition suitable for fabricationinto a radio frequency weldable film structure, the compositionconsisting essentially of a blend of a copolyamide and a polyolefin thathas a carboxylic acid anhydride functionality, the blend having adielectric loss factor of at least 0.05 at a frequency of 27 megahertzat 23° centigrade, the copolyamide being present in an amount with arange of from 20 to 80 percent by weight, based on total blend weight.2. The composition of claim 1, wherein the copolyamide is derived from adimeric fatty acid.
 3. The composition of claim 1, wherein thepolyolefin has polymerized therein at least one monomer that is anethylenically unsaturated carboxylic acid anhydride.
 4. The compositionof claim 1, wherein the polyolefin is a base polyolefin having graftedthereto at least one monomer selected from the group consisting ofethylenically unsaturated carboxylic acid anhydrides.
 5. The compositionof claim 4, wherein the base polyolefin is selected from the groupconsisting of linear low density polyethylene, low density polyethylene,ultra low density polyethylene, copolymers of ethylene and at least onealpha-olefin monomer, linear ethylene/alpha-olefin copolymers,substantially linear ethylene/alpha-olefin copolymers, propylenepolymers and copolymers and copolymers of ethylene and less than 30weight percent, based on copolymer weight, of a polar monomer.
 6. Thecomposition of claim 5, wherein the polar monomer is selected from thegroup consisting of vinyl acetate, methyl acrylate, acrylic acid andmethacrylic acid.
 7. The composition of claim 5, wherein thealpha-olefin monomer contains from 3 to 20 carbon atoms.